Hyperlipidaemia has been recognized as the major risk factor in causing cardiovascular diseases due to atherosclerosis. Atherosclerosis and other such peripheral vascular diseases affect the quality of life of a large population in the world. The therapy aims to lower the elevated plasma LDL cholesterol, low-density lipoprotein and plasma triglycerides in order to prevent or reduce the risk of occurrence of cardiovascular diseases. The detailed etiology of atherosclerosis and coronary artery diseases is discussed by Ross and Glomset [New Engl. J. Med., 295, 369-377 (1976)]. Plasma cholesterol is generally found esterified with various serum lipoproteins and numerous studies have suggested an inverse relationship between serum HDL-cholesterol level and risk for occurrence of cardiovascular disease. Many studies have suggested an increased risk of coronary artery diseases (CAD) due to elevated LDL and VLDL-cholesterol levels [Stampfer et al., N Engl. J. Med., 325, 373-381 (1991)]. The other studies illustrate protective effects of HDL against progression of atherosclerosis. Thus, HDL has become a crucial factor in treating diseases with increased levels of cholesterol [Miller et. al., Br. Med. J 282, 1741-1744 (1981); Picardo et al., Arteriosclerosis, 6, 434-441 (1986); Macikinnon et al., J. Biol. Chem. 261, 2548-2552 (1986)].
Diabetes is associated with a number of complications and also affect a large population. This disease is usually associated with other diseases such as obesity, hyperlipidemia, hypertension and angina. It is well established that improper treatment can aggravate impaired glucose tolerance and insulin resistance, thereby leading to frank diabetes. Further, patients with insulin resistance and type 2 diabetes often have raised triglycerides and low HDL-cholesterol concentrations and therefore, have greater risk of cardiovascular diseases. The present therapy for these diseases includes sulfonylureas and biguanides along with insulin. This type of drug therapy may lead to mild to severe hypoglycemia, which may lead to coma or in some cases may lead to death, as a result of unsatisfactory glycaemic control by these drugs. Recent addition of drugs in the treatment of diabetes are the thiazolidinediones, drugs having insulin-sensitizing action. Thiazolidinediones are prescribed alone or in combination with other anti-diabetic agents like troglitazone, rosiglitazone and pioglitazone. These are useful in treating diabetes, lipid metabolism but are suspected to have tumor-inducing potential and cause hepatic dysfunction, which may lead to liver failure. Further, serious undesirable side-effects have occurred in animal and/or human studies which include cardiac hypertrophy, hema dilution and liver toxicity in a few glitazones progressing to advanced human trials. The drawback is considered to be idiosyncratic. Presently, there is a need for a safe and an effective drug, to treat insulin resistance, diabetes and hyperlipidemia. [Exp. Clin. Endocrinol. Diabetes: 109(4), S548-9 (2001)]
Obesity is another major health problem being associated with increased morbidity and mortality. It is a metabolic disorder, in which excess of fat is accumulated in the body. Although, its etiology is unclear, the general feature includes excess of calorie intake than it is consumed. Various therapies such as dieting, exercise, appetite suppression, inhibition of fat absorption etc. have been used to combat obesity. However, more efficient therapies to treat this abnormality is essential as obesity is closely related to several diseases such as coronary heart disease, stroke, diabetes, gout, osteoarthritis, hyperlipidaemia and reduced fertility. It also leads to social and psychological problems. [Nature Reviews: Drug Discovery: 1(4), 276-86 (2002)]
Peroxisome Proliferator Activated Receptor (PPAR) is a member of the steroid/retinoid/thyroid hormone receptor family. PPAR∝, PPARγ and PPARδ have been identified as subtypes of PPARs. Extensive reviews regarding PPAR, their role in different diseased conditions are widely published [Endocrine Reviews, 20(5), 649-688 (1999); J. Medicinal Chemistry, 43(4), 58-550 (2000); Cell, 55, 932-943 (1999); Nature, 405, 421-424 (2000); Trends in Pharmacological Sci., 469-473 (2000)]. PPARγ activation has been found to play a central role in initiating and regulating adipocyte differentiation [Endocrinology 135, 798-800, (1994)] and energy homeostasis, [Cell, 83, 803-812 (1995); Cell, 99, 239-242 (1999)]. PPARγ agonists would stimulate the terminal differentiation of adipocyte precursors and cause morphological and molecular changes characteristic of a more differentiated, less malignant state. During adipocyte differentiation, several highly specialized proteins are induced, which are being involved in lipid storage and metabolism. It is accepted that PPARγ activation leads to expression of CAP gene [Cell biology, 95, 14751-14756, (1998)], however, the exact link from PPARγ activation to changes in glucose metabolism and decrease in insulin resistance in muscle has not been clear. PPARα is involved in stimulating β-oxidation of fatty acids [Trends Endocrine. Metabolism, 4, 291-296 (1993)] resulting in plasma circulating free fatty acid reduction [Current Biol., 5, 618-621 (1995)]. Recently, role of PPARγ activation in the terminal differentiation of adipocyte precursors has been implicated in the treatment of cancer. [Cell, 79, 1147-1156 (1994); Cell, 377-389 (1996); Molecular Cell, 465-470 (1998); Carcinogenesis, 1949-1953 (1998); Proc. Natl. Acad. Sci., 94, 237-241 (1997); Cancer Research, 58, 3344-3352 (1998)]. Since PPARγ is expressed in certain cells consistently, PPARγ agonists would lead to nontoxic chemotherapy. There is growing evidence that PPAR agonists may also influence the cardiovascular system through PPAR receptors as well as directly by modulating vessel wall function [Med. Res. Rev., 20 (5), 350-366 (2000)].
PPAR α agonists have been found useful in the treatment of obesity (WO 97/36579). Dual PPAR α and γ agonists have been suggested to be useful for Syndrome X (WO 97/25042). PPAR γ agonists and HMG-CoA reductase inhibitors have exhibited synergism and indicated the usefulness of the combination in the treatment of atherosclerosis and xanthoma (EP 0753 298).
Leptin is a protein when bound to leptin receptors is involved in sending satiety signal to the hypothalamus. Leptin resistance would therefore lead to excess food in-take, reduced energy expenditure, obesity, impaired glucose tolerance and diabetes [Science, 269, 543-46 (1995)]. It has been reported that insulin sensitizers lower plasma leptin concentration [Proc. Natl. Acad. Sci. 93, 5793-5796 (1996): WO 98/02159)].
A number of compounds belonging to β-aryl-α-hydroxypropanoic acids and their derivatives have been reported to be useful in the treatment of hyperlipidemia, hypercholesterolemia and hyperglycemia [U.S. Pat. Nos. 5,306,726, 5,985,884, 6,054,453, 6,130,214, EP 90 3343, PCT publications Nos. WO 91/19702, WO 94/01420, WO 94/13650, WO 95/03038, WO 95/17394, WO 96/04260, WO 96/04261, WO 96/33998, WO 97/25042, WO 97/36579, WO 98/28534, WO 99/08501, WO 99/16758, WO 99/19313, WO99/20614, WO 00/23417, WO 00/23445, WO 00/23451, WO 01/53257].